The generator stator core is the largest component in the train of a turbine generator set. The stator cores are generally manufactured from thousands of laminations of relatively thin steel plates which are stacked, pressed and clamped together into the large cylindrical form of the stator core. Typically, the stator core is assembled from the steel plates directly at the final installation site. However, the large size of the stator core and the need for proper clamping results in stator core manufacturing difficulties, including generous floor space and high crane requirements. U.S. Pat. No. 5,875,540 by Sargeant, which is incorporated herein by reference, overcame some of the problems with the prior art by first assembling a number of laminations into a distinct set, referred to as a donut, and then stacking these donuts to form a stator core. This saved great amounts of time over assembling the laminations individually, and produced a stator core with less flaws. When the individual laminations, or the set of laminations in a donut, are installed into a core, they engage what are referred to as keybars. Keybars are essentially rods that run the internal length of the stator core and provide a hook-in spot for the laminations. Laminations are inserted within the stator frame, engaging keybars and are stacked together to form the stator core. An end-on view is shown in FIG. 1 of a stator core 10. Since it is assembled, the laminations that make up the core are not separately discernable from this perspective. The core is held to its frame (not shown) by keybars 6, but the core itself is held together by thru-bolts 12, which are literally long metal bolts that extend through the length of the core, keeping all of the laminations together.
One advantage of using donuts is that the core can be stacked horizontally, rather than vertically as is the common practice. Stacking the core horizontally saves large amounts of time and effort. When the cores were being stacked vertically, a center post was placed down the middle of the assembling core and variation was measured against this reference. When the core is stacked horizontally, however, the use of a center post becomes problematic. Therefore, although stacking the core horizontally can largely be a better practice than vertical stacking, there remain some difficulties in the practice.
What is needed is a method and apparatus that allows for an improvement in checking stator core alignment. Particularly what is needed is an improvement in checking stator core alignment for a core that is being assembled horizontally.
Other difficulties with the prior art also exist, some of which will be apparent upon further reading.